This invention generally relates to manual wheelchairs, and more specifically concerns a new wheel assembly for a manual wheelchair.
According to current statistics, there are more than 1.4 million full-time manual wheelchair users in the United States. The population of individuals using wheelchairs is currently estimated to grow at a rate of approximately 10 percent per year for at least the next several years. While reasons for using a wheelchair, and more specifically a manual wheelchair, vary significantly, manual wheelchair users typically have a lower extremity weakness, paralysis or, in some cases, amputation, which makes walking either impossible, unsafe or very difficult.
Causes of these lower extremity conditions vary widely, but include spinal cord injuries, hemiplegia and other types of paralysis, multiple sclerosis, cerebral palsy, spinal bifida, arthritis and lower limb amputations, among others. There are also several millions of people per year who are temporarily in wheelchairs for several weeks or more during recovery from injury, surgery or illness.
A user""s success with a wheelchair, as well as their independence and, in particular, their community access, is significantly affected by their ability to self-propel the wheelchair. While some individuals with manual wheelchairs have access to personnel to propel a wheelchair on their behalf, it is usually desirable for the users themselves to be able to independently propel their wheelchair.
Interestingly, given the rapid acceleration of technology in many areas affecting modern life, including advances in assisting people with various disabilities in various ways, and significant advances in the areas of vision and hearing improvement, as well as development of various new medical procedures and equipment, there has been little change in the basic design of manual wheelchairs over the past 150-200 years.
With manual wheelchairs, the user propels, steers and brakes the wheelchair by either pushing against or grasping a hand rim portion (also known as a push rim) of the wheelchair. The hand rim is structurally connected to the wheelchair wheel, which in turn contacts the ground. Typically, the user must apply a relatively large force to accomplish many conventional wheelchair actions. Those actions may result in various acute and chronic arm and shoulder repetitive stress injuries. For instance, shoulder-related injuries have been shown to afflict up to 51 percent of manual wheelchair users, while elbow, wrist and hand injuries and pain are also widely noted. Some injuries/conditions, while generally regarded as minor, are still painful, such as blisters and calluses on the user""s hands, due to sliding friction between the hand rim and the user""s hands (especially during extended braking).
Various environmental conditions can accentuate or even cause such injuries, including poor or uneven terrain or surfaces affected by inclement conditions such as rain, snow and ice, as well as cold or slippery hand rims. In many cases, the incidence of such injuries to an otherwise healthy (albeit incapacitated) user can hasten the time of transition to a powered wheelchair or the necessity of an attendant. An attendant is generally undesirable, as independence is usually highly valued by wheelchair users and results in reduction of already scarce resources.
A number of attempts have been made in the past to improve manual wheelchair performance and decrease the burden on the user in his/her use of the wheelchair. These include two-speed or multi-speed wheelchairs, such as shown in U.S. Pat. Nos. 5,482,305 and 5,160,156, among others. Various drive mechanisms are known, including arm cranking systems such as shown in U.S. Pat. Nos. 5,037,120 and 4,506,901, in which cranks and gears similar to a bicycle are mounted in front of the rider and are turned by the hands to propel and brake the wheelchair. Another system uses a central planetary gear drive, such as shown in U.S. Pat. Nos. 5,486,016 and 5,362,081, while lever drives, such as shown in U.S. Pat. Nos. 4,682,783, 5,941,547 and 5,322,312, are also known. A more recent development is known as the electrical assist manual wheelchair wheel. However, these designs and features and others like them suffer from various disadvantages, including expense, inconvenience, substantial additional weight and difficulty of installation on existing wheelchairs.
Also, while there are numerous patents involving various wheelchair braking systems, no system has a successful automatic (and readily overridable) xe2x80x9choldingxe2x80x9d action as a wheelchair is being pushed up a hill, to prevent the wheelchair from rolling backwards as a user advances his grip on the hand rim. Reliable, mechanically efficient braking for downhill movement has also been a troublesome and challenging issue for wheelchair designers. A bicycle-type coaster brake for wheelchairs is known (U.S. Pat. No. 5,160,156), but it does not have hill-holding capability.
Hence, several aspects of a manual wheelchair are in need of improvement, including better multi-gear arrangements, better gear shifting arrangements, a holding capability for uphill movement and better braking for downhill movement, with such improvements being capable of easy installation on existing wheelchairs. Some of these needed improvements apply to powered wheelchairs or wheelchairs using power assist wheelchair wheels as well.
Accordingly, the present invention is a two-speed drive mechanism for a wheelchair, comprising: a wheelchair wheel; a hand rim which permits a user to drive the wheelchair wheel; a gear assembly which includes a first gear arrangement for driving the wheelchair in a first, 1:1 gear ratio, and a second, hypocycloidal gear arrangement for driving the wheel in a second, lower gear ratio than 1:1; a support assembly for mechanically linking the hand rim and the gear assembly; and means for shifting between the two gear arrangements.